This invention relates to wheel end assembly, and more particularly to a wheel end assembly for an inverted portal axle as used in a mass transit vehicle.
Mass transit vehicles, such as trolley cars, buses, and the like typically have seats aligned at the lateral sides of the vehicle, with a central aisle and floor extending along the vehicle. In order to facilitate entering and exiting from the vehicle, it is desirable to have the vehicle floor and aisle positioned relatively low to the ground. This provides faster cycle time during stops and facilitates boarding for all passengers, especially for elderly and disabled passengers as well as for children.
Mass transit vehicles typically have several axles that support, drive and steer the vehicle. Many such vehicles provide a rigid axle having an input positioned off-center near one wheel end to form an inverted portal axle configuration. The input to the portal axle rotates about a longitudinal axis and is typically low to the ground to allow the vehicle floor to be as low as possible. The output to the wheels defines a lateral axis that is vertically higher than the longitudinal axis for the input.
This inverted portal axle includes a short axle shaft member that drives the wheel end near the input and a long axle shaft member that drives the opposite wheel end. The portal axle further includes a pair of gear assemblies, one gear assembly positioned at each wheel end, to raise driving input from each of the axle shafts up to the vertically higher output position at the wheels. Typically this gear assembly includes a gear housing, an input gear driven by the respective axle shaft, an output gear for driving the wheel, and a pair of intermediate gears in meshing engagement with the input and output gears.
The output gear drives a wheel shaft that is enclosed within a spindle that is mounted to the gear housing. A wheel hub is mounted for rotation relative to the spindle and receives driving input from the wheel shaft. A brake spider is also mounted to the gear housing to support a brake input member. This traditional configuration incorporates at least three bolted joints and four bearings to support the rotating components. Assembly time and overall component cost is significant due to the large number of components and complexity of this configuration. Also, the large number of components and the fasteners needed for the bolted joints increase the overall weight in the vehicle, which can significantly affect fuel economy.
Accordingly, it is desirable to provide a simplified wheel end assembly for a portal axle configuration to reduce weight, cost, and assembly time in addition to overcoming the other deficiencies in the prior art discussed above.
A wheel end assembly includes a gear housing with a gear assembly that drives an output shaft. The output shaft is attached to a wheel hub that drives a vehicle wheel. A tube is press-fit into the gear housing and extends into a wheel hub cavity to provide support for wheel bearings. The bearings are mounted directly between the tube and the wheel hub to support the wheel hub for rotation relative to the spindle.
The tube defines a first engagement surface and the gear housing defines a second engagement surface. The first and second engagement surfaces are in contact with each other to create a retaining contact pressure between the tube and the gear housing to prohibit axial movement between the tube and the gear housing.
In the preferred embodiment, the gear assembly includes an input gear driven by an input shaft and an output gear in driving engagement with the output shaft. A set of intermediate gears transfers driving force from the input gear to the output gear. The output shaft is received within the tube with an inboard end splined to the output gear and with an outboard end attached to the wheel hub. Thus, the output gear, the output shaft, and the wheel hub all rotate relative to the tube and gear housing.
In one disclosed embodiment, the gear housing includes a main portion and a cover portion that attach at an interface to define a gear case joint. The gear case joint can be inboard or outboard of the gear assembly depending upon the configuration of the input, output, and intermediate gears. The gear housing includes a main wall with a transversely extending cylindrical portion. The cylindrical portion includes an inboard end that extends inwardly from the main wall toward the gear assembly and an outboard end that extends outwardly from the main wall toward the wheel hub. The cylindrical portion has an inner bore surface that defines the second engagement surface.